Sender load control



o. MYERS 2,351,446

I SENDER LOAD CONTROL I Filed Deo. 22, 1942 6 Sheets-Sheet 1 June 13, 1944.

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June 13, 1944. Q MYERS 2,351,446.

SENDR LOAD CONTROL Filed Dec. 22, 1942 l 6 ySheets-Sheet 4;'`

/A/L/ENTOR OMVERS BV @6M A T TORNEV' June 13,1944 o. MYERS SENDER LOAD CONTROL Filed Dec. 2.2; 1942 e ysheets-Sheet 5 TOR By awa/es M A TTORNEY June 13, 1944. o. MYERS 2,351,446

SENDER LOAD CONTROL Filed Dec. 22, 1942 e sheets-sheet e- K D b Q: s e

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gall-lll I BY -O;MVER$ Patented June 13, 1944 SENDER LOAD CONTROL Oscar Myers, Mount Vernon, N. Y., assignor to s Bell Telephone Laboratories, Incorporated, New

' York, N. Y., a corporation of New York Application December 22, 1942, Serial No. 469,787

8 Claims.

Thisv invention relates to telephone systems and has for its object to-reduce the ill effects of peak load conditions.

- In a cross bar system, the switches are directed in their action by control devices, senders and markers. These control devices are of two kinds,

originating and terminating, the former receiving the complete designation of the wanted -line and connecting the calling line to a trunk incoming to the oihce at which the wanted line is located. The terminating sender receives the numerical designation from the originating sender and with the help of the terminating marker controls'the connection of the incoming trunk to the wanted line, thereby completing the connection between the calling and called lines.

Telephone exchanges are designed to complete all calls lduring heavy load periods with a certain minimum of delay. Throughout the greater part of the time, therefore, there Will be no delay. Occasionally, however, some event of exceptional interest will produce such a congestion of calls that the control equipment will all be busy and calls will experience long delay. When such a condition arises, any action which tends to increase the holding time of the sender adds to the congestion.

In the setting up of a conneotionin the cross bar system, the subscriber usually dials seven digits all of which are recorded in the originating sender. The first lthree digits are transmitted to the originating marker which uses them to determine the identity of the wanted oflice, to operate a plurality of cross bar switches to connect the originating sender with the wanted oiiice and to transmit to the sender an indication of the type of ,oiiice to which the `call is going and with which the connection has been established. The originating sender cannot start to transmit the numerical digits to the distant office until itreceives this indication from the :marker and it can only transmit; the digits as fast as they are recorded in the sender. However, it is apparent that under normal conditions some of the numerical digits will have been recorded during the operation of the marker and the remaining digits will be received promptly. The sender is designed to make a brief pause between successive digits to allow time for the necessary interdigital operations at a mechanical terminating oice and, in the case of a properly dialed designation, the last digit will ybe recorded by the time'the sender is ready to sendit out. `Both the originating sender and. the terminating sender are provided with timing means for timing their complete .op-

eration but these intervals are made long enough to permit even very slow dialing to be completed. However, in the case of traffic congestion, if the subscriber stops dialing without restoring his receiver, both the originating sender and the terminating sender will be held out of service until the timing means complete their operations.

In accordance with the present invention means is provided by which a predetermined interdigital delay will bring about the release of the terminating sender. Furthermore, this release means is rendered effective only in the case of an overload condition in which vall terminating senders of the ofce are simultaneously busy for more than a predetermined length of time.

The invention will be more clearly understood from a consideration of the following description in connection with the drawings, in which:

Fig. 1 shows in diagrammatic form the connection between an originating subscriber and the terminating sender, as well as the sender link control circuit and the timing equipment;

Figs. 2, 3 and 5` show the control circuits of the terminating sender;

Figs. 4 and 6 show the cross bar register of the terminating sender; and

Fig. 1A shows the manner in which the other figures should be arranged.

A complete disclosure of the originating' circuits of a cross bar oice may be found in United vStates Patent 2,235,803 granted March 18, 1941, to W. W. Carpenter, while the terminating circuits are disclosed in United States Patent 2,- 089,921, granted to W. W. Carpenter. on August 10, 1937. t

When the subscriber at substation IUD initiates a call, the substation is connected over line switches to an idle district junctor and over the line switches and sender link to an idle originating sender. He then dials the designation of the wanted line. Having received the designation of the wanted oice the sender connects by means of a marker-connector with a marker. lThe marker controls the operation of the district and ollice switches to extend the calling line to an incoming trunk at the wanted `oflice.

At the .wanted oiliceVthe sender link control circuit selects anl idle terminating sender which may be assumed to be the sender shown. rThe sender link then operates relay followed in turn by relay 104. With relay 104' operated, the frame designating leadsja're connected to theselect magnets 900, etc. and to lrelays 300 and 3N. Either relay 300 or relay 3 l 0 in operating extends its operating `ground to conductor 2l5, operating relay 201 which in turn operates relays 203 and 204.

With relay 204 operated a circuit is closed for operating relay 20| through its upper winding from ground supplied over conductor I1I5 by the link control circuit. Relay 20| connects ground to conductor 2I0 operating the sender-busy relay IIO in the link circuit.y RelayY IIO, in operating, connects ground to conductor Itll'thereby operating sloW-to-release relay |20 and preparing a circuit for relay 202.

When one of the select magnets, for example magnet 904, operates to register the units, digit of the frame identification, it extends its operating ground over conductor v91|v to the winding of relay 30| and battery. Relay 30| locksunder the control of relays 306 and 2I8 and closes a circuit for operating relay 208 which locksto conductor 2 5. Relay 208, in operating, closes a circuit from. battery through the winding of frame hold magnet 4I0back contact of holdmagnet 41|conductor IN2-,front ,contactv of relay 208back. contact of relay- 2I1 to the windings of relay 2I8. Relay 2-I8 isdifferentiallywound andA will not operate on current flowing through both windings eyen- Withthe hold. magnetv connected in parallel with its upper Winding. When theframe designation has beenl properly registered the circuit of relay 202 is completed. `Relay-202 operates and locks under the-control of'relay20 I= and provides a holding circuit for relay 20| under the control of release` relay- 102.` Relay 202 alsoy connects ground to conductor 2435,-to holdl the linkl switches operated.

With relay 20| operated,.connecting ground to v conductor 2-I9,V the circuit for the holdr magnet ill-- is extended throughr the lower winding of relay 2| 8'tov ground'on conductor 2.I,9 and magnet 4I0- operates locking to conductor 2I5which. is now also grounded by relay I. Differential relayi 218 isV energized through itsY upper winding' alone and operates, opening one3loeking circuit for relay rIhe sender is now ready to receive-the nu.- merijcal designation of-.thef Wantedlline; To this end a pulsing circuit is establishedfromi battery through .theI windingv of; relay 302;- upper front contact of relay 201, norrnaLcont'acts: of; relays; 2 HI1 and 2-I3,.the inner upper front contact/,of .relay 20 I over theY tip.- contacts offthle: sender linkswitches. andk the. oflice .andi district;` switches, through the` district; junctor. and; the. sender link at'Y the originating officer. to the, pulsing relay ofl the originating sender andi backovertheri'ng contacts of the same switches to the inner lower. fronti contact ofgrelay 20|, upper back contact. of relay 206to the'winding of :relay 11| 3 andV ground; If the. originating sender is ready-to transmitthe. firstV numericalV digit this circuit will: be. com,- pleted and relay 302' 'operates together, with; the. pulsing relay of the: originatingsender. Relay H3 cannot operate at once, since itswinding is shunted by ground `connected.tolconductor 301: over the inner rightbackcontact ofxrelay 3.06? and over the right back`V contact of relayf305.. Relay- 302 closes a circuitfrom ground' at its frontconf tact over the-outer right-back contact ofrelay 306, middle-upperfrontcontact of relay 30| toi-the winding of relay 305 and battery. Relay 305operates andeV locksover its inner right contact to ground at the: contact. ofA relay 302; disconnects one ground from.; conductor-` 301V,v andlcloses anv obvious circuituior relay 306,. Relay 30Iroperates and opens the-.secondglocking circuit; forI relay 30| causing that relaytofrelease; y

Relay 306 opens the second shunt around relay 1I3, which now operates, closing a circuit from battery through the winding of relay 1 I 5, over the upper back contact of relay 105, front contact of relay 1 I3, lower back contact of relay 105 to ground. Relay 1I5 operates, closing two circuits, one from ground over its upper contact to the winding of relay 302, holding that relay operated andI shunting the" pulsing relay of the originating sender and the pulsing relay 1 I 3 of the terminating sender, thereby sending one revertive pulse to the originating sender. The second circuit controlsk the counting relays 32| to 326 and may be traced over the lower contact of relay 1I5, contact of jack 1I6-, conductor 1I1,l over the left back contact of relay 308 to the Winding of relay 3II and battery. Relay 3II operates and closes a locking circuit from battery through its winding, right winding of relay 308, back contact of relay 300, front contact of relay 3II to ground at the front contact o-f relay 305. Relay 308 cannot operate in this circuit being shunted byground on conductor 1 I 1. Y

When relay 1I3releasesin response to the closure of theshunt by relay 1I5-, relay 1|5 is re,- leased in turn, permitting relay 1I3 to reopera-te. The reoperationof relay 1I=3 causes the reoperation of relay 1I5 and these relays continue to operate alternately until the pulsing circuity is opened at the originating4 sender. WhenV relay- 1 I 5 releases, relay 308 operates in the locking cir.- cuit abovetraced. At the second operation. of relay 1I5, ground on conductor 1'I1f extends over the left front contact and left winding of relay- 308 to the right winding of relay 300 and.- bat ductor 1I1, both, relays 309 and: 308 release so that the cycle ofoperations by relays 30|),v 309- and 3| I is repeated for each pair of pulses-from` relay 1I5'.

With relays 305 and 306 operated, groundiis connectedrto the rig-ht armatures. ofV relay 306. While relay 308-is1released ground is extended to conductor 3I2 and while relay 308 is operated ground is extended ,to conductor '3| 3'. The-counting relaysl 32| to 326 operate under the4 controloi: relay 308 to -record-the-number of revertivepulses transmitted to the originatingjsender. When the originatingsender has. beenr satised, thepulsing. circuit is opened. and: relay 302- releases followed by relays 30,5- arrd; 30.61 With relay: 306'released one of: the; selectma'gnete of: the register' of Figs.` 4-.and. 6 is operated?. under. the control. ofy the countingV relays; operating; relay. 30I-- as. before: At this-time relay 30|- releases-relay 208i and the: hold magnet' III-I oi-v the rst digit vertical lsoperated' in themannerdescribed for the'f-rame" vertical.v

`When the originating sender'is ready to r'eceive the next digitythe pulsing circuit is4 reclosed, operating relay 302., With4 relayf30l op"- erated to indicate' that a previous digit has been transferred' to aselect' magnet of' ther register, relay '305. operatesin turn operatingrelay 306'. For the further operation ofthesender reference is made'to the above-mentioned Carpenter Patent 2,089,921.

, However, froxnfthe Vforegoing it will be appar` ent that the interdigital interval occurringbee tween the completion of the'-r registration of lone digitv and. the start. of the.' next digit.' may* be` measured by the release and reoperation of re-y lay 30.5. l y As previously described, the operation of relay 20| connects ground to conductor 2|0 operating `the sender-busy relay H in the sender link control circuit. Relays H and H9 are sender- -busy relays vbelonging to other senders of the same sender. group and, when operated, in turn operate sloW-to-release relays |25 and |29. When all of the senders of a group are busy, a chain circuit is closed from ground over the lower contactsof relays ||9,` H5, H0 and the intermediate relays of the group through the winding of group relay |30 to battery. Relay |30, in turn,.operates relay |3| which is slow to release. When the group of slow relays |20 to |29 are all operated they close a supplementary circuit for relay |3|. .f Similar groups of busy and slow relays are provided for the other sender groups which, when operated to indicate a group-busy condition, in turn operate relays 32, |33, etc. With allof the sender groups busy, a chain circuit over the contacts of relays |3|, |32, 33, etc. is closed, connecting ground to conductor |34. The purpose of the supplemental slow-to-release re-` lays is to prevent the removal of ground from .conductor |34 during the brief intervals which occur between the release of the sender by one call and its seizure on the next call when trafic is heavy. The individual slow relays tend to bridge this momentary idle period and the group relay adds an additional bridging interval.

.When ground is connected to conductor |34, a circuit is completed for relay |40, which controls the timing circuit. Relay |40 operates and connects ground over its outer right contact-to conductor |4| preparing a circuit over interrupter |42 for relay |43. Relay |43 operates at each Closure of the interrupter |42, locks to the back contact of meter |44 and operates that meter, thereby obtaining an indication of the 'duration of the all-senders-busy condition. At

left contact, ground is extended over the right contact of relay |5|, back contact of relay |52, to the winding of relay |49 and battery. Relay |49 also locks lunder the control of relay |40 and connects the right contact of interrupter |48 -to the winding of relay |52, which relay operates -when that interrupter Contact is closed and locks -to relayv |40. With relayl |52 operated, interrupter |48 next closes a circuit from ground over 'its left Contact, right frontcontacts ofA relays |5| and |52 to the left winding of relay |50 and battery. Relay |50 operates and locks in a circuit from battery through its right winding and right front contact to ground at the back -contact of relay |53. Interrupter |48 has a co-mvplete' cycle of 7 seconds with a 5-secondinterval `between the closure of itsleft contact and the .closure of its right contact. Therefore the time between the grounding of conductor |34 and the operation of relay |50 will vary between 12 and ,19 seconds. If desired, the time .may be shorte'ned by omitting relays |49 and |52 thereby omitting one complete cycle of operation by the interrupter. v

With relay |50 operated, lamp |54 is'lighted and a circuit is closed from ground at the inner right contact of relay |40, inner left contact of relay 50 to the winding of relay |55 and battery. With relay |55 operated, a circuit is closed from ground on .conductor 103, left contact` of relay 123 which is normally closed, lower back contact of relay 120, conductor |56, front contact of relay |55, conductor |51 to interrupter 290.

From the foregoing it will appear'that, when an all-terminating-senders busy condition has existed for a predetermined length of time, interrupter 290 is rendered effective by connection of ground to its contact. Relay |55, and such other relays as are necessary to close the proper number of contacts, closes a similar circuit for each sender of the oilice. When interrupterV 200 closes its right contact it completes a circuit from ground on conductor |51 through the winding of relay 20| to battery through resistance 390. Relay 29| operates and locks over its lower contact to conductor |51. Since the ground for conductor |51 was obtained from conductor 103 of this same sender, interrupter 290 cannot become effective until relay 202 has operated and the sender is ready to receive the iirst digit. As soon as the pulsing circuit is closed at the originating sender, relay 302 operates as above described in turn operating relay 305. Relay 305 at its inner left contact connects grounded conductor |51 to resistance 390 in shunt of the winding of relay 29|, causing that relay to release. At the end of the digit, when the originating sender opens the pulsing circuit, relays 302 and 305release as above described and-relay 29| again operates as soon as the interrupter 200 closes its right contact, only to be released when the pulsing circuit is closed for the'next digit.

After the units digit has been recorded the originating sender should reclose the pulsing circuit to receive a reverse battery pulse generated by the terminating sender. Relay 29| would de tect a delay in this closure. Relays 302 and 305 are operated during the reverse battery closure, thereby rendering relay 29| ineffective at that time. After the release of the originating sender, relay is operated from the trunk circuit, disconnecting ground from conductor |56 and thereby from conductor |51 so that the sender is permitted to complete its operation in the normal manner.

If, now, there is a considerable delay in the reclosure of the pulsing circuit, relay 29| is permitted to remain operated until interrupter 200 closes its left contact, thereby completing a circuit from ground on conductor |51 over the left contact of interrupter 290, top contact of relay 29|, to the winding of trouble-release relay 10| and battery. Relay 10| locks to grounded oonductor 103, opens the start circuit for the marker-connector and brings about the release of the terminating sender in the manner described in the above-mentioned Carpenter Patent 2,089,921.

When the busy condition is relieved for long enough to permit one of the slow group busy relays 3|, |32 or |33 to release, relay |40 releases, permitting relays |49, |52, |5| and |55 to release also. Since relay |50 is locked under the control of relay |53, that relay remains operated and the release of relay |40 closes acircuit from ground! at the back contact of relay |40, middle left contact of relayl |50,`conductor |58 tothe armature of interrupter |59. Interrupter |59'in closing its right contact operates relay |60which locksto conductor |58. With relay |'60operated, the next closure of the left contact of interrupter |59 operates relay |53 which also locks toconductor' |58. Relay |53, inV operating, opens' the locking circuit of relay |50 which releases, restoring the timing circuitto normal. Interrupter |59 has a 30-second cycle so that the restoration of the load control lcircuit will be delayed from 30 to 60 seconds in order to hold relay' |55 ready for immediate reoperation should the relief of the congestion' be only temporary. After relay |50 releases, an all-senders-busy condition must continue long enough to reoperate relays I5 |49, |52 and |50 in order to operate relay |55 and render the interdigital timing interrupter elTective. While relay |50 is held operated temporary relief of the load will permit relay |55 to release but the recurrence of the overload will immediately reoperate relay |55. The reoperation of relay |40 in response to the renewal of the all-senders-busy condition removes ground from conductor |58 so that a complete release timing cycle Will occur after each cessation of the overload.

From the foregoing description it will be apparent that under normal operating conditions neither the timing arrangement of Fig. 1 nor the interdigital release means will function. However, in the casey of trailic congestion such that all of the terminating senders become busy and the all-senders-busy condition continues for as much as 12 to 19 seconds, it renders the interdigital timing feature effective and a delay of 3 to 'seconds in the receipt of any digit, which is indicative that the number has been only partially dialed, will bring about the release of the terminating sender. If the call is abandoned, relay 120, which operates to prevent the seizure of the marker, also d-isablesthe interdigital timing interrupter. v

When no congestion exists, a sender which-encounters trouble is released under the controlof interrupter 229 and relays 230 and 2M, but the cycle of interrupter 229 requires 30 seconds to complete. It is therefore apparent that the interdigital timing arrangement of the present inven tion shortens the sender holding time in the case of partial dialing.

If the long interdigital time interval is due-to an interruption of the dialing, the originating sender holds the pulsing circuit open until the next digit comes in. It then recloses the pulsing circuit causing the incoming trunk circuit to seize another sender. Since part of the digits stored on the originating sender haveV already been transmitted, the sender cannot transmit a'complete number to the se'condsend'er andthe interdigital time out will release: the second sender, if the all-senders-busy condition continues.

What is claimed is:

1. In. a telephone system.. a register sender, means to seizesaid.: senders.. register.contini-,means in said sender, means for repeatedly operating and releasing said register controlmeansv during the registration of cachot apl'urality of' digits,

timing means, means toi start the operationof said timingA meansV at eachreleaseof saidjregis'- ter control meanst and to releasek said" timing meansA at each operation of said register control means; andmeans under-thecontrol of said tim lll ing in'eanseifectiveto releasesaidlsender ifv more than a predetermined time elapses between' suc cessive digit-registrations;

2. In a telephone system, a' registerV sender, means tov seize said sender; means in said sender for registering a plurality of digits comprisinga pulsing circuit, means to close said pulsingcircuit to start the transmission of each digit, means to. open said pulsingy circuit in response to the complete` transmission of eachl digit, a relay included in said pulsing circuit, timing means, means under control of said relay to start the operationof said timing means at each opening.

of` said pulsing circuit and to release said timing means at each closure of rsaid-pulsing circuit, and means underthe control,` of said timing meansto release'said sender if said pulsing circuit remains open more than a predetermined lengthof time.

3. In a telephonersystem, a pluralityv of sendersV means to seize one of said senders, means in sai-d sender for registering a plurality of dig;- its comprising a pulsingv circuit, means to close said pulsing circuitl to start the transmissionof each digit, means to open said pulsing circuit in responseA to thecomplete transmission of each digit, a relay yincluded in said pulsing circuit, means under the control of said relay to release said sender if said pulsing circuitv remains open more than a predetermined length of time,v and means to render said releasing means effectiveonly when a predetermined number of said senders are busy. K

4. In a telephone system, a plurality of senders, means to seize one of said senders, means in said sender for registering a plurality of digits comprising a pulsing circuit, means to closesaid pulsing circuit to start the transmission of each digit, means to open said pulsing circuit in respouse to the complete transmission of each digit, a relay included in said pulsing circuit, means under the control of said relay to release said sender if said pulsing circuit remains open more than a predetermined length vof time, and-means to render said releasing means effective only i. when an all-senders-busy conditioncontinueslfor a'predetermined length of time.

5. In a telephone system, a plurality of senders, means to seize one of said senders, means in said sender for registering. a plurality of digits comprising a pulsing circuit, means to close said pulsing circuit to start the transmission of each digit, means to open said pulsing circuit in response to the complete transmission of each digit, a relay included in said pulsing circuit, timing means under the control of said. relay, means under the control of said timing means toy release said sender, anclv means to rendersaid releasing means effective only when a predetermined number of said. senders are busy.

6. In a telephone systemaplurality of senders, means to seize each of said senders, means to markeach sender busy in response to said seizure, register control means ineach sender, means for repeatedly operating said register control means duringthevregistration of each of a plurality of digits, -timing meanseiective to release a sender if more than a predetermined time elapses be.- tween successive operations of saidregister control'means, means responsive tothe joint oper.- ation of the busy markingr means of all of' said senders to render said' timing means effective, and other means to render saidtiming means ineiective after said plurality ofi digits has been registered.

7. In a telephone system, a pluralityofsenders.

means to seize each of said senders, means to mark each sender busy in response to said seizure, register control means in each sender, means for repeatedly operating said register control means during the registration of each of a plurality of digits, timing means effective to release a sender if more than a predetermined time elapses between successive operations of said register control means, means responsive to the joint operation of the busy marking means of all of said senders to render the timing means in each sender effective, and means individual to each sender to render said timing means ineffective after said plurality of digits have been registered in each of said senders.

8. In a telephone system, a register sender, means to seize said sender, means in said sender for registering a plurality of digits comprising a pulsing circuit, means to close said pulsing circuit to start the transmission of each digit, means to open said pulsing circuit in response to the complete transmission of each digit, a relay included in said pulsing circuit, timing means, means under control of said relay to start the operation of said timing means at each opening of said pulsing circuit and to release said timing means at each closure of said pulsing circuit, said relay also rendering said timing means inoperative during closures of said pulsing circuit, and means under the control of said timing means to release said sender if said pulsing circuit remains open more than a predetermined length of time.

OSCAR MYERS. 

